THIS INVENTION relates to a planar transformer. It also relates to a method of optimizing a planar transformer.
With the advent of new technology there is a constant drive to make products which are more compact. In certain electronic equipment the power supply with its associated transformer occupies a relative large volume, particularly where relatively high power is to be delivered with multiple output voltages. Reducing the physical size of the transformer may thus be advantageous.
According to a first aspect of the invention, there is provided planar transformer which includes
a primary winding; and
a secondary winding defined by a first stage including at least one track on a first layer and at least one track on a second layer which in combination provide a first output voltage, and a second stage including at least one track on the first layer and at least one track on the second layer which in combination provide a second output voltage, wherein the ratio of maximum cumulative current in the first and second stages is equal to half of the ratio of the track widths of the first and second stages.
The first stage may include at least one track on the first layer and at least one track on the second layer each for opposite output current and the second stage may include at least a pair of tracks, one on each layer, each for opposite output current.
The tracks associated with the first stage may be connected in series with the tracks associated with the second stage and the voltage across the first stage may form part of the voltage of the second stage.
A single pass of a track through a core of the transformer may provide a segment voltage and the segments may be connected in series to form at least one string of voltage segments with voltage output tapping points.
The tracks and their associated segments are typically printed circuit board tracks similar to those used in conventional planar transformers.
The transformer may include at least two voltage strings which start at the same point and pass through the core of the transformer in opposite directions so that the voltage strings are mirror images of each other thereby to balance the core.
The two voltage strings may provide voltage tapping points having opposite polarities.
The planar transformer may include at least one source of flux generated by at least one primary winding connected in a series or parallel configuration.
The first stage may be configured to provide an output voltage of about 3.4 V from the tracks of the first stage, and the second stage may be configured to provide an output voltage of about 5.1 V from the tracks of the first stage together with the tracks of the second stage.
The planar transformer may include at least one further output voltage stage.
According to another aspect of the invention, there is provided a planar transformer which includes
a primary winding; and
a secondary winding defined by at least two tracks, wherein the ratio of maximum cumulative current in the tracks is equal to half of the ratio of the track widths.
According to a further aspect of the invention, there is provided a method of enhancing electrical or physical characteristics of a planar transformer, the method including
designing a primary winding which is capable of inducing a preselected minimum voltage in a secondary winding of the transformer; and
designing the secondary winding so that it includes first and second tracks, wherein the ratio of maximum cumulative current in the first and second tracks is equal to half of the ratio of the track widths of the first and second tracks.
According to yet a further aspect of the invention, there is provided a method of enhancing electrical or physical characteristics of a planar transformer, the method including
designing a primary winding which is capable of inducing a preselected minimum voltage in a secondary winding of the transformer; and
designing a secondary winding so that it includes a first stage including a first track on a first layer and a second track on a second layer which in combination provide a first output voltage, and a second stage including a third track and fourth track on the first layer and a fifth track and sixth track on the second layer which in combination provide a second output voltage, wherein the ratio of maximum cumulative current in the first and second stages is equal to half of the ratio of the track widths of the first and second stages.
Conventional planar transformers which have E-type cores are manufactured in standard sizes. Thus the present invention may be used to optimize the electrical or physical characteristics of a planar transformer which uses a standard core.
In a preferred embodiment of the invention, the planar transformer is configured for use in computer equipment such as a personal computer or PC. Accordingly, the first stage may be configured to provide an output voltage of about 3.4 V from two single turns which each pass through the core once, and the second stage may be configured to provide an output voltage of about 5.1 V from three single turns i.e. a further single turn connected in series to the two single turns of the first stage. In a similar fashion, the transformer may also include further stages, e.g. a third stage to provide about 11.9 V.
The invention is now described, by way of example, with reference to the accompanying diagrammatic drawings.